1. Field of the Invention
The present invention relates to an optoelectronic material and device application, and a method for manufacturing an optoelectronic material, and more specifically, to an optoelectronic material formed from luminescent silicon (Si)—a substance with an inexhaustible supply and that causes no environmental pollution—as its core, and further characterized by excellent compatibility with Si-LSI technology, self-luminescence, and stability, and a manufacturing method therefore.
2. Description of the Prior Art
As Si is an indirect transition semiconductor, and its bandgap is near the infrared region, at 1.1 eV, it has not been thought possible to use it as a light emitting device in the visible region. In 1990, however, visible light emission at room temperature was confirmed with porous Si (e.g. L. T. Canham, Applied Physics Letters; Vol. 57, No. 10, 1046 (1990)). Since that time, research on visible light emission at room temperature with Si as the base material has become quite popular. As the vast majority of these reports have concerned porous Si, this luminescent porous Si will be described as an example of the prior art.
Basically, luminescent porous Si is formed by anodizing the surface of a single-crystal Si substrate with a solution comprising hydrofluoride mainly. Up to the present, photoluminescence (PL) has been confirmed at a number of wavelengths in the visible light region, from 800 nm (red) to 425 nm (blue). There have also been recent attempts to generate electroluminescence (EL) through current injection excitation. These technologies have been disclosed, for example as described in Japanese Patent Laid-Open Publication No. Hei. 4-356977 and Japanese Patent Laid-Open Publication No. Hei. 5-206514.
Some of the hypotheses proposed to explain the luminescence mechanism of Si, which is an indirect transition semiconductor, are: that among the porous shapes are nanometer (nm) order three-dimensional microstructure regions, which cause a loosening of the wave frequency selection rules, causing a radiative electron-hole recombination process; and that a Si polycyclic oxide (siloxane) is formed on the surface of the porous Si, and on the interface between this siloxane and Si is a new energy level that contributes to the radiative recombination process. But at any rate, it appears certain that with regard to optical excitation effects, a quantum confinement effect changes the energy band structure (broadening the gap width).
With conventional technology, however, the creation of a Si microstructure like porous Si increases the proportion of atoms exposed on the surface, making the luminescent characteristics dependent on the surface state. Si easily oxidizes, and oxidation of the surface changes the band structure, changing the luminescent wavelengths and degrading the luminescent intensity. This problem is particularly striking with porous Si, because of the instability of the hydrogen termination on the surface.